Unit D: Mechanical Systems

1. Unit D: Mechanical Systems

2. Topic 1: Levers and Inclined Planes • Lever: a simple machine that changes the amount of force you must exert in order to move an object • Contains a bar that is free to rotate around a fixed point (fulcrum) • The fulcrum supports the lever

3. Levers and Inclined Planes • Effort force: the force that you exert on a lever to make it move • This is the force given to any machine to produce an action • Load: the mass of an object that is moved or lifted by a machine such as a lever • This is the resistance to movement that a machine must overcome

4. Levers and Inclined Planes • Effort arm: the distance between the fulcrum and the effort force • Load arm: the distance between the fulcrum and the load

5. Classes of Levers • Depends on the position of the effort force, load, and the fulcrum • Class 1 Lever: the fulcrum is between the effort and the load • This class of lever can be used for power or precision • Ex. scissors

6. Classes of Levers • Class 2 Lever: theload is between the effort and the fulcrum • Always exerts a greater force on the load than the effort force you exert on the lever • Ex. wheelbarrow

7. Classes of Levers • Class 3 Lever: the effort is exerted between the fulcrum and the load • You must exert a greater force on the lever than the lever exerts on the load • The load can be moved very quickly • Ex. Hockey stick

8. Bones and Muscles: Built-in Levers • Your bones act as levers, and your joints act as fulcrums in your body • Most levers in your body are class 3 levers, but also contain some class 1 and class 2 levers. • Ex. Moving your head up and down (class 1), standing on your toes (class 2), moving your arm up and down (class 3)

9. An Arm in Space • The Canadarm is used to launch and recover satellites, has repaired the Hubble Space Telescope, and maintains the International Space Station • It operates by a series of gears and levers

10. Mass vs. Weight • Recall the difference: • Mass: a measure of the amount of material in an object • Measured in grams (g) or kilograms (kg) • Does not change! • Weight: a force your body exerts on the Earth • Measured in Newtons (N) • Changes depending on where you are!

11. What is work? • When aforceis exerted on an object causing it to move in the direction of the applied force, work is being done Work = Force X Distance • Work is measured in Joules (J) • Force is measured in Newtons (N) • Distance is measured in meters (m)

12. Examples 1. A force of 2.0N was applied to a lever, and it moved a distance of 0.6m. Calculate the work done on the lever. 2. A force of 16.2N was applied to a wheelbarrow, and it moved a distance of 8.25m. Calculate the work done on the wheelbarrow.

13. The Inclined Plane • Inclined plane: a ramp or slope that reduces the force you need to exert to lift something • A machine!

14. Work Input and Work Output • Input work: the work YOU do on the machine • Output work: the work the MACHINE does on the load • A machine NEVER does more work on the load than you do on the machine • Machines make work easier because they change the size or direction of the FORCE exerted on the machine

15. What is Mechanical Advantage? • Mechanical advantage: the comparison of the force produced BY a machine (LOAD FORCE) to the force applied TO the machine (EFFORT FORCE) • Comparing the size of the load to the size of the effort force Mechanical Advantage (MA) = Load Force (FL) N Effort Force (FE) N *There are NO UNITS for MA because it is a RATIO! • Mechanical advantage can be >1, =1, or <1

16. Examples • If you apply a force of 500N to a branch, and a car you are trying to lift weighs 2500N, what is the mechanical advantage of the branch-lever? • How many times easier did the branch make lifting the car? • You exert a force of 736N while riding your bike by pushing the pedals. The force needed to move the bike forward is 81N. What is the mechanical advantage of the bike? • What is the mechanical advantage of moving a flag up a flagpole if the effort force required is 120N and the load force is 120N?

17. Another way to calculate MA - We can use levers to illustrate mechanical advantage Mechanical Advantage (MA) = Effort Arm Load Arm • The longer an effort arm is on a lever, the easier it will be to do work on the load • The longer effort arm gives you mechanical advantage Example: If the effort arm of a branch-lever is 3m and the load arm is 0.3m, what is the mechanical advantage of the branch-lever?

18. Speedy Levers - The advantage of a class 3 lever is that the force will move the load a greater distance at a faster speed • Speed: the rate of motion, or the rate at which an object changes position

19. Machines Made to Move • Ergonomics: the science of designing machines to suit people

20. Topic 1 Review p. 284 #1-5

21. Topic 2: The Wheel and Axle, Gears, and Pulleys A Lever That Keeps on Lifting • Winch: a simple machine that consists of a small cylinder, a crank (handle), and a cable. Used for lifting and pulling. • The axle of the winch is held in place and acts like a fulcrum • The handle is like the effort arm of a lever • Exerting an effort force on the handle turns the wheel

22. A Lever That Keeps on Lifting • Radius: distance from the center of the wheel to the circumference • The radius of the wheel is like the load arm of a lever • The force that the cable exerts on the wheel is like the load on a lever • Other examples: Pencil sharpener, fishing rod

23. The Wheel and Axle • A winch is an example of a wheel-and-axle device • Wheel and axle: a simple machine consisting of two turning objects attached to each other at their centers. One object causes the other object to turn. • This machine also provides a mechanical advantage

24. Speed and Action • A wheel-and-axle device can also generate speed • They require a large effort force and produce a smaller force on the load

25. Gearing Up • Gear: a rotating wheel-like object with teeth around its edge • Gear train: a group of two or more gears • Driving gear (driver): first gear in a gear train, may turn because its attached to a handle or motor • Driven gear (follower): second gear, driven by the first gear

26. Going the Distance • Sprocket: a gear with teeth that fit into the links of a chain

27. Going the Distance • Each link of a bicycle chain moves the same distance in the same period of time • Ex. If a front sprocket has 45 teeth and does one full rotation, the back sprocket with 15 teeth will have to turn three times for each time the front sprocket does • Speed Ratio: the relationship between the speed of rotations of a smaller gear and a larger gear Speed Ratio = Number of driver gear teeth Number of follower gear teeth

28. Examples • A bicycle has a driver gear with 150 teeth and a follower gear with 25 teeth. What is the speed ratio of this bicycle? • A machine has a driver gear with 40 teeth and a follower gear with 5 teeth. What is the speed ratio of this machine?

29. Pulleys • Pulley: a grooved wheel with a rope or chain running along the groove • Similar to a class 1 lever • The rope acts like the bar and the axle like the fulcrum

30. Pulleys • Fixed pulley: is attached to something that does not move • Ex. A ceiling, wall, tree • Can change the direction of the effort force • Ex. Flagpole pulley • Movable pulley: attached to something else (often a rope), the load may be attached to the center of the pulley

31. Pulleys

32. Supercharging Pulleys • If we compare a pulley to a lever, we’ll find that the load arm and effort arm are the same • Combinations of pulleys are required to lift heavy and awkward loads • Block and tackle: a combination of fixed and movable pulleys; may be used to lift very heavy or awkward loads • Can have a very large mechanical advantage • Compound pulley: a combination of several pulleys working together

35. Topic 3: Energy, Friction, and Efficiency Work and Energy How many simple machines have we explored? • Work is a transfer of energy • Kinetic energy: the energy of motion • Ex. Energy is transferred throughout a bicycle • Energy cannot be created or destroyed, it can only be TRANSFERRED • Where does the energy come from in a refrigerator? • Where does the energy come from when you ride your bike?

36. Stored Energy • Energy must be transferred to a machine in order for the machine to work • Sometimes, this energy needs to be stored • Potential energy: stored energy • Ex. Chemical potential energy, gravitational potential energy, mechanical potential energy • Fig. 4.26

37. Energy Transmitters • Energy can be converted from one form to another • Energy can also be transmitted • Transmission: energy is transferred from one place to another, and no energy is changed or converted • Ex. Electrical wires in your home, chain connecting two sprockets on a bicycle

38. No Machine is 100% Efficient • Ideally, a machine would transfer ALL of the energy it received to a load or other machine • However, some of the energy is always lost • The work output of a machine is always LESS than the work input Work Input > Work Output YOU always put more effort into the machine than the machine puts on the load

39. No Machine is 100% Efficient • Efficiency: how much of the energy you gave to a machine was transferred to the load by the machine • Efficiency is a comparison of the useful work provided BY a machine or system with the work supplied TO the machine or system • Efficiency is measured as a percentage (%)

40. No Machine is 100% Efficient Efficiency = Work done by lever on load X 100% Work done on lever by effort force • The higher the efficiency, the better the lever is at transferring energy • A “perfect” machine would be 100% efficient • However, the efficiency of real machines is never 100% because every time a machine does work, some energy is lost to friction

41. No Machine is 100% Efficient Work done = Work done + Energy lost as ON a machine BY the machine heat due to friction • Many machines can be made more efficient by reducing friction • Ex. Adding a lubricant such as oil or grease

42. Boosting Efficiency • Some effort force put into a machine is used to overcome friction • Ex. On a bicycle, you must overcome the friction of the gears rubbing together • Keeping the gears lubricated with oil or grease, and properly inflating tires will reduce friction in a bicycle

43. Useful Friction • We need friction for machines to work properly • Can you imagine a world without friction? • Examples: • Curlers use brooms to decrease friction • Sports players use powder on their hands to improve their grip • Shoes are designed to keep us from slipping when we run or walk over varied terrain

44. Topic 3 Review p. 302 #1-3 – as a class Topic 1-3 Wrap-Up p. 303 # 1 – 20 - for marks!

45. Topic 4: Force, Pressure, and Area • Force: a push or pull, anything that causes a change in the motion of an object • Area: the amount of surface; measured in square units (cm2) • Pressure: the force acting perpendicular to a certain surface area

46. Calculating Pressure Pressure (N/m2 or Pa) = Force (N) Area (m2) • Pressure is measured in N/m2 or Pa (Pascal) • 1 kPa = 1000 Pa • Ex. If a force of 800N is exerted on an area of 1.2m2, what is the pressure? • Ex. If a student weighs 45kg, and occupies a space of 0.98m2, what is the pressure exerted on the ground?

47. Equipped Against Pressure • Protective sports gear helps to distribute a force over a large area. This lessens the force of the impact and decreases the potential for injury. • Explain how an air bag acts to protect a driver

48. Pascal’s Law • Pascal’s Law: pressure exerted on a contained fluid is transmitted equally in all directions throughout the fluid and perpendicular to the walls of the container • The shape of the container has no effect on pressure

49. Pascal’s Law • Hydraulic lift: a mechanical system that uses a liquid under pressure in a closed system (self-contained) to raise heavy objects • Ex. Vehicles in a service station, circulatory system, forklift • Fluid used in machines is usually oil – water is not a good lubricant and tends to rust parts of the machine • Each cylinder has a platform (piston) that rests on the surface of the oil

50. Pascal’s Law